汚染: pollution

area, district, particular geographic region

serious, deep, heavy (topic), profound (change), weighty (matter)

seriousness

blue line / (historical) Short for 青線地帯(あおせんちたい) (aosenchitai): Aosen (districts in Japan where prostitution and the sex industry flourished)

question, problem on homework etc. / a question; a matter (of time etc.) / a problem (something that needs to be dealt with); a trouble / an issue; a matter

汚染水: polluted water

becoming more serious

become more serious

chemical pollution